Which file associates GIDs with group names?

A.
/etc/group

B.
/etc/groups

C.
/etc/system

D.
/etc/default/group

Explanation:

The /etc/group file associates GIDs with group names. Files /etc/groups and /etc/default/group do not exist. The file /etc/system is a kernel configuration file.
The format of the /etc/group file is:
Group name : password (if any) : list of group members separated by commas